Frequency or phase shift demodulator



May 23, 1967 J. E. RUSSELL Re. 26,210

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May 23, 1967 J. E. RUSSELL Re. 26,210

FREQUENCY OR PHASE SHIFT DEMOUULATOH Original Filed July V, 1959 3Sheets-Sheet ATTORNEYS May 23, 1967 J. E. RUSSELL 3 Sheets-Sheet l;

Original Filed July 'f'. 1959 NVENTOR. JAMES E. RUSSELL AT TORNEYSuUnited States Patent() 26,210 FREQUENCY 0R PHASE SHIFT DEMDULATOR JamesE. Russell, Tulsa, Okla., assignor to United Aircraft Corporation, acorporation of Delaware Original No. 3,044,020, dated July 10, 1962,Ser. No.

825,586, July 7, 1959. Application for reissue June 30, 1964, Ser. No.392,983

17 Claims. (CI. 329-103) Matter enclosed in heavy brackets appears inthe original patent but forms n0 part of this reissue specification;matter printed in italics indicates the additions made by reissue.

This invention relates to improvements in FM subcarrier signal detectorsfinding great utility in telemetering systems, and is particularlyconcerned with eliminating the adverse effect of white noise, commonlyexperienced in long range radio transmission, thereby to increase thesensitivity of the detector to small radio signals and hence increasethe range of radio transmission of intelligence without a proportionalincrease in the transmitting power.

It is accordingly a primary object of the invention to provide a systemfor detecing FM subcarrier signals under noise conditions sufficientlygreat as to render the signals normally unintelligible with conventionaldetectors.

In known radio telemetering systems for use in cornmunicatinginformation over long distances through air and space, considerableeffort has been directed toward increasing the power of the transmitterand improving the efficiency of the transmitting and receiving antennas,as well as improving the detecting systems in an effort to extend therange or distance of radio communication. Where the transmitter isairborne or spaceborne aboard an aircraft or missile, the problemsinvolved in increasing the radiated power produced by the transmitterbecome particularly acute since this involves a considerable increase inthe size and weight of the transmitter, as well as in its power supplyand associated equipment. Further` more, as the range of communicationis increased, the noise signals become progressively more troublesomeand as a result it is more essential that the detectors are made moresensitive and selective to reject the spurious noise signals and respondonly to the desired intelligence being transmitted.

It is accordingly a further object of the invention to provide animproved FM subcarrier detector for increasing the transmission range ofa given telemetering system without requiring a change in thetransmitting equipment.

A still further object of the invention is to provide an FM detectoroperable with a smaller signal to noise ratio.

A still further object is to provide such a detector that is small,lightweight, and compact for aircraft and related uses and thatpossesses a minimum number of operating components.

A still further object is to provide such a detector that is completelytransistorized and temperature compensated.

Other objects and many attendant advantages will he more readilycomprehended by those skilled in the art alter a detailed considerationofthe following specification taken with the accompanying drawingswherein:

FIG. l is an electrical block diagram representation of one preferred FMdetector according to the present invention,

FIG. 2 is a diagram illustrating the electrical waveform being producedin the various circuits of FIG. l,

FIG. 3 is an electrical schematic diagram illustrating one preferredamplifier and limiter that may be employed in the detector of FIG. lI

FIG. 4 is an electrical schematic diagram illustrating a preferredmaster oscillator that may be employed in FIG. l,

FIG. 5 is an electrical schematic diagram illustrating Re. 26,210Reissued May 23, 1967 lCC preferred gate circuits, differentialamplifier, and filter circuits that may be employed in the detector ofFIG. l, and

FIG. 6 is an electrical schematic diagram illustrating a preferredamplifier that may be employed in the detector of FIG. l.

Referring now to the drawings for a detailed consideration of onepreferred detector system according to the present invention, there isshown in FIG. l a block diagram representation of the various componentcircuits and their manner of interconnection, and in FIG. 2 a series ofwaveforms, labeled A to H, inclusive, depicting, in sequence, thevarious changes in the received signal as it passes through thereceiver.

Initially in the usual frequency modulation telemetering system, thereis transmitted a number of channels or frequency bands carryingintelligence, and each employing a different subcarrier frequencyoperating in or near the audio frequency band. Consequently, thecomposite transmitted signal containing the several subcarrier frequency modulated signals is first directed over an input line 10 to anamplifier 1l having a bandpass filter for selecting the desiredsub-carrier signal and providing the necessary amplification thereof.The output of amplifier l1 is therefore a frequency modulated subcarriersignal generally having the waveform A, as illustrated on the uppermosttime scale in FIG. 2. As generally shown by waveform A in FIG. 2, thisfrequency modulated signal is not a continuously variable FM signalhaving a true sinusoidal waveform and a constant peak amplitude as wouldbe desired, but rather is quite jagged in waveform, fluctuating at anygiven time over a rather wide range due to the noise signals also beingreceived and arnplied by the amplifier 1l.

The selected FM subcarrier signal obtained from amplifier 1I andcontaining the noise signal is then directed to a limiter circiut 12which provides the function of clip ping or limiting the amplitude ofthe signal, to provide essentially square wave, constant amplitudepulses of varying pulse width and spacing therebetween corresponding tothe received FM signal, as depicted by waveform B in FIG. 2.

Observing waveform B more closely, it is noted that each pulse usuallyhas a number' of leading edges and a number of trailing edges. Thiscondition results from the fact that in the signal as illustrated, thereceived noise signals are quite large with respect to the intelligencesignal whereby as they pass through the limiter 12 along with theintelligence signal, their effect is to blur or obscure the leadingedges and trailing edges of the clipped intelligence pulses by producingshort spikes or impulses before and after the intelligence pulses. Forthis reason known FM detectors experience considerable difficulty indistinguishing between the noise and intelligence signals, and ininstances where the noise components are as large in relation to theintelligence as shown in waveform B, known detectors are unable toclearly distignuish between the two.

According to the present invention, however, there is provided adetecting means ulrich does not rely upon determining the exact locationand time relation of the leading edges of the pulses for deriving thetransmitted intelligence from the signal but rather relies upon thepulse width and other characteristics of the unidirectional impulses ofwaveform B, whereby the presence of the noise spikes at the edges of thepulses does not obscure the intelligence.

Returning again to FIGS. l and 2 for an understanding of this new mannerof distinguishing the desired intelligence from the noise signal, thereis provided a variable frequency master oscillator unit, such as amultivibrator 13, as shown, which is adapted to operate within the samefrequency band as the selected FM modulated subcarrier signal, and isautomatically regulated by the unidirectional intelligence pulses(Waveform B) in such manner as to change frequency in correspondencewith the change in frequency of the transmitted FM modulated subcarrier.In other words, there is provided a master oscillator 13 that iscontrolled to change frequency With the received FM signal and hencesimulate the operation of the oscillator in the FM transmitter, wherebythe signal varying the master oscillator 13 may then be used to derivethe desired intelligence without interference from the large noisecomponents.

The master oscillator 13 produces two series of square wave pulses overlines 14 and 15, with the first series of pulses over line 14 being 180electrical degrees in advance of the impulses over line l5, and withboth series of pulses being 90 electrical degrees out of phase with theunidirectional intelligence pulse (waveform B), as shown in FIG. 2.

The first series of standard impulses (waveform C) over line 14 isdirected upwardly to turn on and off a gate circuit 16 and the secondseries (Waveform D) over line 15 is directed to a similar gate circuit17. Since the standard pulses over line 14 are 180 electrical degrees inadvance of those over line 15, it is evident that gates 16 and 17 areopened and closed in alternating sequence (in response to these pulses).That is, when gate 16 is opened gate 17 is closed, and the reverse. Theintelligence pulses from limiter 12 (waveform B) are also directed toenergize both gates 16 and 17, and these intelligence pulses or portionsthereof alternately pass through the gates 16 and 17 in sequence, as thegates are alternately opened by the standard pulses over lines 14 and15.

Assuming that the frequency variation of master oscillator 13 is thesame as the received FM subcarrier wave, and that the standard pulsestherefrom being directed over lines 14 and 15 are exactly displaced 90degrees therefrom as shown in waveforms B, C, and D of FIG. 2, then thefirst half of each intelligence pulse (waveform B) will be passed bygate 16 over its output line 18 and the second half of each intelligencepulse of waveform B will be passed by gate 17 over its output line 19.This first half of the pulse is represented by waveform E in FIG. 2, andthe second half thereof is represented in FIG. 2 by waveform F. In otherwords, assuming that the master oscillator 13 is in synchronism with theFM subcarrier, the clipped FM signal (waveform B) is divided into twoequal parts, with the first part substantially equalling the first halfof each pulse (waveform E) being transmitted by gate 16 over line 18 andwith the second part, equalling the second half of each pulse (waveformF) being transmitted by gate 17 over line 19.

Continuing this assumption of synchronism between the master oscillator13 and received FM subcarrier signal, it is evident that the energycontained in the first half pulses over line 18 must equal the energycontained in the second half pulses over line 19 and consequently if thepulses over line 18 are integrated and the result subtracted from theintegrated pulses over line 19, the result would be zero, indicatingthat the master oscillator 13 is in synchronism with the received FMsubcarrier signal.

On the other hand, if the received FM subcarrier signal varies, themaster oscillator 13 loses synchronism with this signal, with the resultthat the FM signal is no longer divided into two equal energy pulsetrains over lines 18 and 19, as before, but rather the pulses over line18 may have either a greater pulse width than those being transmittedover line 19 or a lesser pulse width depending upon the direction ofchange of the FM intelligence signal. Consequently as the received FMsignal varies, the energy contained in the pulses over line 18 increasesor decreases with respect to that of the pulses over line 19, andsubtracting one from the other provides an error signal representing thedifference in frequency between the received FM signal and that ofmaster oscillator 13.

To complete the follow-up loop and provide a continuous measure of thechange in the received FM signal, this error signal being produced overline 20 is directed backwardly to energize the master oscillator 13 insuch manner as to increase or decrease the frequency thereof and againbring the master oscillator 13 into synchronism with the received FMsignal. Thus there is provided an electrical servo or follow-up systemto continuously maintain synchronism between a master oscillator 13located in the FM detector system and that being located remotely in theFM transmitter (not shown). Since this error signal over line 20 servesto modulate or change the frequency of the master oscillator 13 toconform or bring it into synchronism with the transmitted FM subcarriersignal, it is evident that the error signal over line 20 performs thesame function and must be identical with the remotely locatedintelligence signal modulating the transmitter subcarrier oscillator.Consequently, the error signal over line 20 is also the demodulatedoutput signal from the detector of the present invention and isaccordingly also directed over line 2l and through a low pass filter 22and amplifier 23 to ultimately operate recorders, computers (not shown)or other means as well known in the art to perform its intendedfunction.

Returning to FIGS. l and 2 for a more detailed consideration of thepreferred manner of subtracting the energy of the two pulse trains beingtransmitted over lines 18 and 19 to obtain the desired error signal,lines 18 and 19 are connected to energize a differential amplifier unit24 which serves to invert the pulses over line 19 and add these invertedpulses to those over line 1S to provide a substantially square wavealternating current signal, as shown by waveform G. By inverting orreversing the polarity of one series of pulses over that of the other,it is noted from waveform G that the noise signal spikes in one seriesof pulses are also inverted or made of. opposite polarity than thespikes in the other. This square wave alternating signal (waveforln G)is then directed to a filter 25 which functions to integrate the samethereby to obtain the desired error signal over line 20 (waveform H).Since the noise components of the signal are reversed during each halfcycle of the alternating square wave (waveform G), it is evident thatthese noise signals substantially cancel out one another during theintegration process, thereby substantially eliminating the noise fromthe output signal 20. On the other hand, the opposite polarity pulses(waveform G) being obtained from the two series of pulses (waveforms Eor F) will not be of equal energy content unless no intelligence signalis being transmitted, since, as discussed above, the intelligence signalmodulates or varies the frequency of the FM subcarrier, thereby takingit out of synchronism with the master oscillator 13 to render waveform Gasymmetrical.

Thus according to the present invention, there is provided a masteroscillator or multivibrator 13 in the FM detector, whose frequency iscontinuously compared to that of the received FM signal and thedifference thereof is employed to vary the frequency of the masteroscillator to conform or bring it into synchronism with the varia tionsin the received FM signal. In making this cornparison, the leading edgesof the received FM signal are not directly employed, but rather thepulse width of the individual cycles thereof, with the net result thatthe spurious noise signals or spikes are rejected and thus preventedfrom contaminating the received signal to obscure the transmittedintelligence.

As thus far described, therefore, it is believed evident that theamplitude or magnitude of the noise signals are essentially immaterialin effecting the operation of the receiver, since only the pluse widththereof or, more exactly, the difference between the energy contained inthc leading edge noise spikes and that of the trailing edge noise spikescan affect the error signal or output of the detector. Consequently theFM receiver according to the present invention may respond to signalshaving a considerably higher noise-to-signal ratio than known FMdetectors and hence respond to FM signals transmitted over greaterdistances than known receivers.

Thus according to the present invention, there is provided a masteroscillator or multivibrator 13 in the FM detector, whose `frequency iscontinuously compared with the received FM signal and the differencethereof is ernployed to vary the frequency of the master oscillator 13in such manner as to conform or bring it into synchronism with thevariations in the received FM signal. In making this comparison, theleading edges of the received FM signal are not directly employed butrather the pulse of the individual cycles is used, with the net resultthat the suprious noise signals or spikes are rejected and therebyprevented from contaminating the received intelligence to obscure thetransmitted intelligence. As thus far described, therefore, it isbelieved evident that the amplitude or magnitude of the noise signals isessentially immaterial in affecting the operation of the receiver, sinceonly the pulse width thereof or, more exactly, the dilfererence betweenthe energy contained in the leading edge noise spikes and that of thetrailing edge noise spikes, can affect the error signal or output of thereceiver. Consequently, according to the present invention, the FMdetector may respond to signals having a considerablyhigher-noise-to-signal ratio than known detectors and hence may respondto FM signals being transmitted over greater distances than presentlyavailable detection.

According to a preferred embodiment of the invention, the system of FIG.1 is preferably comprised of completely transistorized circuits for thepurpose of reducing the size, weight, and power consumption thereof, aswell as improving its shock and acceleration resistance, all of whichare essential for mobile operation in a aircraft or missiles.

Referring to FIG. 3 for a detailed consideration of preferred amplifierand limiter circuits, generally shown as blocks 11 and 12 in FIG. l, thereceived FM signal being admitted over line is first directed through acoupling capacitor 24 and coupling resistor 25 leading to the baseelement of a first transistor 26, of a pair of direct current coupledtransistor amplifiers, including transistors 26 and 27.

The emitter element of transistor 26 is suitably self biased by means ofparallel connected resistor and capacitor 28 and 29 having theiropposite ends connected to ground 30, and the collector element oftransistor 26 is connected to a suitable source of potential existing online 3l, and being connected thereto through a collector resistor 33.The base element of the second transistor 27 is energized by thecollector element of the first transistor 26, and the emitter andcollector elements of the second transistor 27 are connected to abiasing potential and to the power supply line 3l, respectively. Tothermally stabilize the transistors 26 and 27 and to provide the desiredgain control, negative feedback leading from the emitter element oftransistor 27 and through a capacitor is provided backwardly over line34 to energize the base element of the first transistor 26, as shown.

The output of the second transistor amplifier 27, taken from thecollector element thereof is thence transmitted over line 35 and througha coupling capacitor 36 to the input of a multistage band pass filtergenerally designated 37, which serves the purpose of selecting thefrequency band of the desired subcarrier modulated FM signal. As shown,the band pass filter unit 37 may comprise a conventional multistageseries of legs each including capacitors and inductors in appropriaterelation.

As thus far described, therefore, the input FM signal being receivedover line 10 is first amplified by transistors Cil 26 and 27 and thencedirected to a multistage band pass filter to select the desiredsubcarrier signal.

The output of the selected subcarrier FM signal taken from the band passfilter' 37 is thence transmitted over line 38 leading therefrom to thebase element of transistor 39 which in turn is coupled to a secondtransistor 40. The function of transistors 39 and 40 is to provide a twostage high gain saturation clipping of the signal thereby to produce anoutput signal over line -41 having a waveform substantially asillustrated in waveform B of FIG. 2. Tracing this circuit morespecifically, the signal taken from the band pass filter over line 38 isdirected through a coupling resistor 42 and coupling capacitor 43 toenergize the base element of first clipper transistor 39. Transistor 39has its base element suitably biased by being connected to the centraljunction of a potential divider, consisting of resistors 44 and 45connected in series across energized power supply line 3l and groundline 30. This biasing of the base element of transistor 39, togetherwith the self-biasing of its emitter described below, controls theconduction from its emitter to its collector elements in such manner asto clip or limit the FM signal and produces the waveform B of FIG. 2.The selfbiasing of its emitter element is obtained by means of theparallel connected resistor 46 and capacitor 47 interconnecting theemitter element of transistor 39 to ground. The second transistor 40provides the second stage of the high gain saturating clipping functionwhereby the output signal being produced over line 41 is the square wavesignal having the waveform B in FIG. 2.

In FIG. 4 there is shown a preferred master oscillator or multivibratorcircuit, generally illustrated as block 13 in FIG. l. Referring to FIG.4, there is provided two pairs of transistors 48, 49 and 50, 51. Thetransistors of the rst pair 48, 49 are connected in cascade by directlyconnecting the collector element of transistor 48 to the base element oftransistor 49 over line 52; and the second pair of transistors 50 and 51are likewise connected in cascade by connecting the collector oftransistor 5l to the base of transistor 5f) over line 53, as shown.

Feed back connections are also provided in each pair for temperaturestabilization. In the first pair the feed back comprises connecting theemitter element of transistor 49 backwardly tothe base element oftransistor 48 through a resistor 54, conductor and a second resistor'56. In a similar manner in the second pair there is provided a feed backconnection from the emitter of transistor 50 through resistor 57, andover line 58 and through a second resistor 59 to the element oftransistor 51.

Each of these two pairs of cascaded transistors are also connected infeed `back with the other' to form a multivibrator as desired, as suchconnection may be traced from the emitter of transistor 49 over line 60,and thence through capacitor 6l of a tuning unit, and over line 62 tothe base element of transistor 51. Feed back in the opposite directionis provided from the emitter element of transistor 50 over line 63 andthence through capacitor 64 and over line 65 to the base element oftransistor 48.

Both pairs of transistors 48, 49 and Si), 51 are also suitably biasedand energized from the power supply lines' 66 and ground lines 67 tosupply the necessary energizing and biasing to enable the oscillatorcircuit to function as desired. The control signal received over line 20is directed to both the base element o-f transistor 48 in the first pairand to the base element of transistor Sl of the second pair, thereby tovary the frequency of the multivibrator according to the input signalover line 20,

As thus far described, therefore, the preferred multivibrator unit ispreferably comprised of a pair of two stage amplifiers connected back toback with the output transistor of each pair having its emitter elementconnected to the input of the second pair thereby to provide a freerunning multivibrator. The purpose of providing the two stage amplifiersin back-to-back relation, is to provide temperature compensation wherebythe frequency of this multivibrator is substantially invariable over atemperature range of about to 110 F. As generally described above, thefrequency of this multivibrator is controllable over a wide range inaccordance with the input signal received over line 20, To obtain twosquare wave outputs from this multivibrator, each of which is 180 out oftime phase with the other, signals may be taken from the input to thesecond stage of each pair and directed over lines 14 and 15, as shown.By properly selecting values of the components in the circuit of FIG. 4,it has been found that the frequency being produced by the oscillatormay be varied linearly with a variation of the signal received over line20.

In FIG. 5 there is shown a preferred transistor circuit for the gatecircuits 16 and 17 of FIG, l, the differential amplifier circuit 24 ofFIG. l and the connections to the filter unit 25 of FIG, 1. As shown,the two phase displaced standard square wave pulses from mastermultivibrator unit 13 are introduced over input lines 14 and 1S. Thesquare wave master signal over line 14 is directed upwardly through acoupling capacitor 69 and diode 70 which together form a clampingcircuit. Similarly the opposite phase signal over line 15 is directed tocapacitor 71 and diode 72 similarly forming a clamping circuit to passonly pulses of the correct polarity. The voltage existing at thejunction 73 of elements 69 and 7l] substantially has a waveform labeledC in FIG. 2 and the potential at junction point 74 between clampingelement 71 and 72 has substantially the waveform labeled D in FIG. 2.

The standard pulse signal at junction 73 is thence directed to a summingresistance and the standard pulse from junction 74 is similarly directedto summing resistance 76. The summing resistances 75 and 76 are eachconnected to oppositely poled diodes 77 and 78, respectively` formingpart of the gate circuits 16 and 17, respectively of FIG, l. The FMreceived signal being transmitted over line 41 (output of FIG. 3) isdirected to two resistors 79 and 80 each of which has an oppositeterminal connected to the reversely poled diodes 77 and 78,respectively. With this arrangement, whenever the potential at clampingjunction 73 is positive, the signal over line 41 is permitted to passthrough the gate and through a coupling circuit generally designated 8l.to the base of a transistor 82. Similarly, whenever the potential atclamping junction 74 is positive, the input signal over line 41 ispermitted to pass through a coupling circuit generally designated 83 tothe base clement of a second transistor 84. connection with blockdiagram of FIG. l, the multivibrator standard signals being producedover lines 14 and 15 are 180 out of time phase whereby the signals atclamping junctions 73 and 74 are likewise 180@ out of phase.

As a result the clipped and limited FM signal being introduced over line41 is alternately permitted to pass to transistor 82 duringapproximately one-half of each cycle and is alternately permitted topass to transistor 84 during the second half of each pulse cycle.

Transistors 82 and 84 are so connected that transistor 82 inverts orreverses the polarity of imptllses received at its base element andcombines this inverted pulse with the pulse received at the base elementof transistor 84, with the net result that the combined inverted halfpulse and non-inverted half pulse are both summed at the junction 85 andthe signal therefor being transmitted over line 86 thus is substantiallyidentical with waveform G of FIG. 2. Thus the function of transistors 82and 84 is to serve as a differential amplifier for receiving each of thehalf pulses from gate circuits 16 and 17, inverting one of the halfpulses with respect to the other and summing the difference, thereby toproduce the alternating pulse waveform of waveform G of FIG. 2 over line86. The signal over line 86 is then directed upwardly to a low passfilter 25 which effectively integrates waveform As generally describedabove in f lll n 0 G to produce the error signal over line 20 and havinga waveform substantially identical with waveform H of FIG. 2.

As generally discussed above, in connection with FIG. l, the errorsignal being produced over line 20 is proportional to the dilierence infrequency between the received FM signal and the standard frequencysignal being produced by multivibrator 13. This signal is directedbackwardly to control the frequency of the master multivibrator unit 13(over the same line 20) thereby to again bring the frequency of themultivibrator unit 13 into coincidence with the detected FM signal.

The error signal over line 20 is also the desired demodulatedintelligence signal, as discussed above, and is consequently alsodirected to a low pass filter 22 (FIG. l for the purpose of removing anyfurther spurious variation of the subcarrier, and thence is directed toa power ampilfier 23.

One such preferred power amplifier circuit is shown in FIG. 6. In FIG. 6the liltered output signal from low pass lter 22 is received over line87 and directed in cascade through three pairs of transistors 88, 89;90, 91; and 92, 93. Each of these pairs of transistors such as 88, 89are connected in an emitter follower arrangement, with the emitterelement of the first transistor 88 being connected to the emitterelement of the second transistor thereby to provide the first pair. Thesecond pair of transistors 90, 91 is also connected in a similar emitterfollower arrangement, as is the third pair 92, 93. The collector elementof the first transistor 88 of the first pair, is also directly coupledto the base element of the first transistor 90 of the second pair, andthe collector output of the latter transistor 90 is likewise directlyconnected to the base element of the first transistor 92 of the thirdpair. In a similar manner, the collector output of the second transistor89 of the first pair is directly coupled to the base element of thesecond transistor 91 of the second pair, and the collector element ofthe latter is likewise connected to the base element of the secondtransistor of the third pair. With this arrangement, it is evident thatthe three pairs of transistors are connected in a differentialarrangement with the rst transistor element of each pair constitutingone channel and the second transistor element of each pair constitutingthe second channel of a differentially connected multistage poweramplifier. Feed back connections are also provided between the lasttransistor in each channel and the first transistor of that channel, allfor the purpose of providing stabilized feed back in each channel andtem perature compensations. For example, the collector element oftransistor 92 is connected in feed back over line 94 to the input orbase element of the first transistor 88. Similarly, the collectorelement of transistor 93 is connected backwardly in feedback over line95 to the base element of transistor 89. In each of these feed backpaths over lines 94 and 95 there is provided a resistor 96 and 97 and,as shown, the resistance 96 in feed back line 94 may be made variablethereby to permit adjustment or balancing of the feedback signal asdesired.

The output signal over line 98 of the amplier is thus the combinedsignal output from the two channels of the differential power amplifierunit 23 and is therefore regulated and controlled to yield a zero signalwhenever a Zero input signal to the amplifier is received and to providea substantially linear change in output over line 98 in proportion tothe changes in input signal received over line 87.

What is claimed is:

[1. In a frequency modulating carrier detector, a limiter circiut forclipping the signal to produce a substantially square wave output of thesame frequency thereof, a variable frequency master oscillator producinga pair of like frequency standard signals of opposite phase with one ofsaid standard signals being advanced substantially 90 degrees in phasewith respect to the signal and with the other being retardedsubstantially 90 degrees in phase with respect to the signal, first andsecond gate circuits both responsive to said clipped signal with eachbeing energized by a different one of said standard signals each therebyproducing an output proportional to different half cycles of saidclipped signal, means responsive to the output of both gate circuits forinverting one of said outputs and combining the inverted output with theother output to produce an alternating signal, and means for integratingsaid alternating signal to detect the modulating signal] 2. In ademodulator for frequency or phase shiftable signals, means foramplifying the signal and limiting its amplitude, to produce a series ofvariable frequency unidirectional intelligence pulses of substantiallysquare wave shape, means for dividing each said intelligence pulse intotwo half pulses with the first pulse equalling substantially the firsthalf of each said intelligence pulse and the seeond pulse equallingsubstantially the second half thereof, means for inverting each secondhalf pulse and combining it with the first half pulse to produce analternating pulse intelligence waveform, and means for integrating thealternating intelligence waveform to eliminate the noise componentstherein and demodulate the signal to obtain the desired intelligencetherefrom.

3. A detector for determining the variation in phase or frequency of analternating input signal comprising means responsive to said signal toprovide a series of unidirectional impulses of varying frequency andphase corresponding to variations of the input signal, a pair of gatecircuits energized by said unidirectional impulses, time control meansfor actuating said gates to close and open in time sequence whereby afirst portion of each of said impulses passes through one of the gatesand the remaining portion through the other of said gates, and means forintegrating the difference between said first and second portions andenergizing said control means in feedback according to the integrateddifference thereby to vary the time of actuation of said gates to rendersaid first and second input signal portions equal to one another.

[4. In the detector of claim 3, said control means including anoscillator producing two series of signals in phase opposition, andmeans directing one series of signals to energize a iirst gate and thesecond series to energize the second gate] [5. In the detector of claim4 said difference integrating means including means for inverting thephase of the first portion of said input signal with respect to theother, and means integrating the sum of the inverted first portion andsecond portions] [6. A phase detector for determining variation in phaseof a series of unidirectional input impulses, comprising means energizedby a reference signal generating means for separating each of said inputimpulses into two components, each containing a portion of the energy ofsaid input impulse and in summation equalling the energy of the inputimpulses, means for integrating the difference between the first andsecond components to derive an error signal and means varying saidreference signal generating means by said error signal to continuallymaintain the energy contained in said lirst and second components equal,whereby said error signal is proportional to the variation in phase ofsaid input impulse] 7. In a phase shiftable signal demodulator, meansfor limiting the amplitude of the signal to produce substantially squarewave shape pulses that vary in frequency in proportion to thetransmitted intelligence, a master oscillator producing impulses offrequency in the same bandwidth as the signal, means comparing thefrequency of the master oscillator signal with the signal to produce anerror signaLand means for varying the frequency of the master oscillatorby said error signal to bring it into synchonism with the signal wherebysaid error signal con stitutes the desired demodulated intelligencesignal, said comparing means comprising means responsive to said masteroscillator and to said unidirectional pulses for producing two series ofimpulses, each of the same frequency as said pulses, with the pulses ofthe first series being of greater pulse width than those of. the secondwhen the frequency of the master oscillator signals is greater than thatof the signal and with the pulses of the first series being smallerpulse width than those of the second when the frequency of the masteroscillator signals is less than that of the signal, and means fordetermining the difference between the pulse width of the first andsecond series thereby to obtain the desired error signal.

8. In a phase shiftable signal demodulator, means for limiting theamplitude of the signal to produce substantially square wave shapepulses that vary in frequency in proportion to the transmittedintelligence, a master oscillator producing impulses of frequency in thesame bandwidth as the signal, means comparing the frequency of themaster oscillator signal with the signal to produce an error signal, andmeans for varying the frequency of the master oscillator by said errorsignal to bring it into synchronism with the signal whereby said errorsignal constitutes the desired demodulated intelligence signal, saidcomparing means comprising means responsive to said master oscillatorand to said unidirectional pulses for dividing said pulses into twoseries of pulses of the same frequency, with the first series having awaveform substantially identical with the first half of said pulses andwith the second series having a waveform substantially identical withthe second half of the pulses and with the first series having a pulsewidth greater than the second series or less than that of the secondseries depending upon whether the frequency of the master oscillatorexceeds that of the signals or is less than that of the signals, andmeans for integrating the difference between the two series thereby toobtain the error signal.

[9. In a transistorized frequency modulated signal detector, transistormeans for clipping the signal to produce substantially square waveshapepulses, a transistor multivibrator operating in the same frequencybandwidth as the signal, transistor means comparing the frequency of themultivibrator with the signal to produce an error signal, and means forvarying the frequency of the multivibrator by said error signal tosynchronize said multivibrator frequency with the signal, said comparingmeans including a pair of transistor gate circuits, each responding tosaid signal and to said transistor multivibrator for producing a seriesof impulses having the same frequency as said signal, with the pulsesfrom one gate circuit being of greater pulse width than those of thesecond gate when the frequency of the multivibrator exceeds that of thesignal and being of smaller' pulse width than of the second when themultivibrator frequency is lower than that of the signal, and transistormeans for determining the difference between the pulse width of thefirst and second series thereby to obtain the error signal] [10. Meansfor demodulating a phase or frequency shifted carrier signal comprising:a variable frequency transistor oscillator operating in the samebandwidth as the signal, and producing a pair of like frequencyreference signals of opposite polarity, with one reference signal beingadvanced in phase by 90 with respect to said selected signal and theother reference signal being retarded in phase by the same `amount whenthe oscillator is in frequency synchronism with the signal, and meansresponsive to said pair of reference signals and to said signal to varythe frequency of said oscillator with variation in said signal therebyto maintain one of said pair of reference signals advanced in phase andthe other of said reference signals retarded in phase by equal amountswith respect to said signal, said means for varying the frequency of theoscillator including a pair of transistor clamping and gate circuits,each being responsive to the signal and to a different one of saidfrequency reference signals, a pair of transistors in back-to-backrelation with each being energizable by a different one of saidtransistor clamping and gate circuits, and means responsive to theback-to-back arranged transistors for energizing said oscil. lator tocontrollably vary the frequency thereof] [11. Means for demodulating a`phase or frequency shifted carrier signal comprising: a variablefrequency transistor oscillator operating in the same bandwidth as thesignal, and producing a pair of like frequency reference signals ofopposite polarity, with one reference signal being `advanced in phase by90 with respect to said selected signal and the other reference signalbeing retarded in phase `by the same amount when the oscillator is infrequency synchronism with the signal, and means responsive to said pairof reference signals and to said signal to vary the frequency of saidoscillator with variation in said signal thereby to maintain one of saidpair of reference signals advanced in phase and the other of saidreference signals retarded in phase by equal amounts with respect tosaid signal, said means for varying the frequency of the oscillatorincluding a pair of transistor clamping and gate circuits, each beingresponsive to the signal and to a different one of said frequencyreference signals, a pair of transistors in back-to-back relation witheach being energizable by a different one of said transistor clampingand gate circuits, and means responsive to the back-to-back arrangedtransistors for energizing said oscillator to controllably vary thefrequency thereof, said oscillator including two pairs of directlycoupled transistors, `feedback circuit means interconnecting thetransistors of each pair to provide stabilization against temperaturevariation, means interconnecting both pairs in feedback relation throughreactance means, and means responsive to said error signal for varyingthe voltage biasing of `both pairs thereby to vary the frequency of saidoscillator] [12. ln the detector of claim 9, said difierence determiningmeans including a pair of transistors in reversely poled circuitconnection, means interconnecting each of said pair of transistors toreceive impulses from ia different one of the gate circuits, and meansfor averaging the outputs of the opposing transistors thereby to obtainthe error signal] [13. In a detector, a transistor multivib-rator ofvariably controllable frequency in the same bandwidth `as the signal andproducing two series of output pulses of opposite phase, a pair oftransistor gate circuits, each energized by a diterent series of saidoutput pulses and both being responsive to said signal, a firsttransistor circuit responsive to one of said gates and a secondtransistor circuit responsive to the other, said transistor circuitsbeing connected in opposition whereby the output of one is inverted withrespect to the other, and averaging means for averaging the opposingoutputs of said transistor circuits thereby to obtain an error signalthat is proportional to the change in phase of the signal] [14. In afrequency modulated signal detector, a saturation transistor circuit forclipping the received signals, a pair of transistor gate circuitsresponsive to phase displaced standard pulses of substantially the samefrequency as the received signal and responsive to the clipped `receivedsignal for dividing the clipped signal into two parts, transistor means`responsive to the gate circuits for comparing the energy contained inthe two parts and producing an error signal proportional to the energydifierence thereof, a transistor multivibrator ifor producing said phasedisplaced standard pulses, and means for energizing said multivibratorwith said error signal to vary the frequency thereof in such directionas to minimize the error signal] 15. A detector for frequency and phasemodulated alternating current signals comprising: imeans responsive tosaid signals `for producing a series of substantially unidirectionalimpulses corresponding in waveshape and spacing with every other halfcycle of the alternating current signal, said impulses having noisecomponents `at the leading edges and trailing edges of each impulse,time lll controlled means for dividing each said impulse into twounidirectional impulse portions with the tirst impulse portioncorresponding in waveform with the leading half of the impulse and thesecond impulse portion with the trailing half of the impulses, meansintegrating the difference of said rst and second unidirectional pulseprotions, thereby to nullify the noise components at the leading edgesand trailing edges of each impulse, and produce an output error signalcorresponding to the integrated dierence, and means responsive to theerror signal for energizing said time control means to continuously varythe relative `pulse widths of the first and second portions thereby tomaintain said difference at substantially null, whereby said errorsignal corresponds to the demodulated signal.

16. In a demodulator for a frequency or phase modulated alternatingcurrent signal, means responsive to said signal for producing a seriesof unidirectional impulses corresponding in time duration and spacingwith each like polarity half cycle of the alternating current inputsignal, a pair of sequentially operating gate circuits adapted to beoperated during the time interval of each unidirectional impulse forseparating a leading portion of each impulse from a trailing portionthereof, means for integrating the difference between said leadingportion and trailing portion to produce a variable error signal, andmeans responsive to said error signal for continuously controlling thetime of operation of said gates to maintain said leading portion andtrailing portion substantially equal, whereby said variable error signalconstitutes the demodulated output signal.

17. A phase-shift detector including in combination a source of inputalternating current, a variable frequency source of referencealternating current, the input and reference sources having the samemeans frequency and u means relative phase shift of approximately unintegrating low pass filler, means for coup/im;7 the input lrource tothe filter throughout cach half cycle of n cci'- Iuin polarity of thereference source, and means responsive to the filler for controlling thefrequency of the reference source.

I8. A phase-Shift detector including in combination a source of inputalternating current, a variable frequency source of referencealternating current, the input und reference sources having lhc samemean frequency and a mean relative phase shift of approximately 90, agufo, an integrating low-pass ltcr, means coupling the input source tothe gate, means coupling the gute to the filter, nicuns for actuatingthe gate throughout euch half cycle of a certain polarity of thereference source, und means responsive to the filter for controlling thefrequency of the reference source.

19. A phase-shift` detector including in combination u source of inputalternating current, a variable frequency source of referencealternating current, the input and reference sources having the samemean frequency and o mean relative phare shift of approximately 90, agute providing an output, means coupling the input source to the gute,means for actuating the gute throughout cach half cycle of u certainpolarity of the reference source, und means responsive to the gateoutput for controlling the frequency of the reference source.

20. A phase-.Shift detector including in combination a source of aninput alternating current signal, a variable frequency source of areference alternating current signal, the input and reference signalshaving the sume mean frequency und a mean relative phase shift ofapproximately 90, means for providing a detection signal in accordancewith the time integral of those portions of the input signal which areconcurrent with cach half cycle of u ccrluin polarity of the referencesignal, und means responsive to the detection signal for controlling thefrcqucncy of the reference source.

21. A phase-shift detector including in combination a source of asquare-wave alternating current input signal,

the input source comprising a limiter, a variable frequency source of analternating current reference signal, the input and reference signalshaving the same mean frequency and a mean relative phase shift ofapproximately 90, means for providing a detection signal in accordancewith those portions of the input signal which are concurrent with eachhalf cycle of a certain polarity of the reference signal, and meansresponsive to the detection signal for controlling the frequency of thereference source.

22. A phase-shift detector including in combination a source of an inputalternating current signal, a variable frequency source of a referencealternating current signal, the input and reference signals having thesame mean frequency and a mean relative phase shift of approximately 90,means for providing a detection signal in accordance with those portionsof the input signal which are concurrent with each half cycle of acertain polarity of the reference signal, and means responsive to thedetection signal for controlling the frequency of the reference source.

23. A phase-shift detector including in combination a source of an inputalternating current signal, a variable frequency source of a referencealternating current signal, the input and reference signals having thesame mean frequency and a mean relative phase shift of approximately90", means for providing a detection signal in accordance with thedifference between those portions of the input signal which areconcurrent with each positive half cycle of the reference signal andthose portions of the input signal which are concurrent with eachnegative half cycle of the reference signal, and means responsive to thedetection signal for controlling the frequency of the reference source.

24. A phase-shift detector including in combination a source of asquare-wave alternating current input signal, the input sourcecomprising a limiter, a variable frequency source of an alternatingcurrent reference signal, the input and reference signals having thesame mean frequency and a mean relative phase shift of approximately 90,means for providing a detection signal in accordance with the timeintegral of the difference between those portions of the input signalwhich are concurrent with each positive half cycle of the referencesignal and those portions of the input signal which are concurrent witheach negative half cycle of the reference signals, and means rcsponsiveto the detection signal for controlling the frequency of the referencesource.

25. A phase-shift detector including in combination a source of asquare-wave alternating current input signal, the input sourcecomprising a limiter, a variable frequency source of an alternatingcurrent reference signal, the input and reference signals having thesame mean frequency ana' a mean relative phase-shift of approximatelymeans for providing a detection signal in accordance with the timeintegral of those portions of the input signal which are concurrent witheach half cycle of a certain polarity of the reference signal, and meansresponsive to the detection signal for controlling the frequency of thereference source.

26. A phase-shift detector including in combination a source of an inputalternating current signal, a variable frequency source of a referencealternating current signal, the input and reference signals having thesame mean frequency and a mean relative phase shift of approximately 90,means for providing a detection signal in accordance with the timeintegral of the difference between those portions of the input signalwhich are concurrent with each positive half cycle of the referencesignal and those portions of the input signal which are concurrent witheach negative half cycle of the reference signal, and means responsiveto the detection signal for controlling the frequency of the referencesource.

27. A phase-shift detector including in combination a source of asquare-wave alternating current input signal, Ille input sourcecomprising a limiter, a variable frequency source of an alternatingcurrent reference signal, the input and reference signals having thesame mean frequency and a mean relative phase shift of approximately 90,means for provia'ing a detection signal in accordance with the dierencebetween those portions of the input signal which are concurrent witheach positive half cycle of the reference signal and those portions ofthe input signal which are concurrent with each negative half cycle ofthe reference signal, and means responsive to the detection signal forcontrolling the frequency of the reference source.

References Cited by the Examiner The following references, cited by theExaminer, are Of record in the patented file of this patent or theoriginal patent.

ROY LAKE, Primary Examiner.

A. L. BRODY, Assistant Examiner.

